1. Field of the Invention
The present invention relates to apparatus for manufacturing waterproof cable, and more particularly, to an apparatus for filling the interstitial voids of a cable core with a waterproofing compound and sealing the compound in and around the cable core.
2. Background and Prior Art
In the manufacture of communications cable, and more particularly, the manufacture of cables intended to be buried beneath the ground, it is desirable practice to fill the interstitial spaces between the insulated conductors of the core as well as other portions of the cable to prevent the ingress of moisture into the cable core.
One method and apparatus for filling a cable core is disclosed in E. L. Franke, Jr. et al. U.S. Pat. No. 3,767,454, the entire disclosure of which is hereby specifically incorporated by reference. The Franke, Jr. et. al. system discloses a technique whereby a cable core having stranded twisted pairs of insulated elongated conductors is moved longitudinally through a series of in-line chambers having interconnecting dies to facilitate the evacuation of air from voids in the interstitial structure of the core and the pressure application of a waterproofing compound of jelly-like consistency into the air evacuated voids. Thereafter, the compound filled cable core may be passed through various stations where core wrap and sheathing materials are placed about the core in combination with additional applications of the waterproofing compound. A plastic jacket is extruded about the sheathing and is cooled prior to takeup of the jacketed cable onto a reel.
In the application of the core wrap and sheathing materials to a cable core filled with waterproofing compound in accordance with the Franke, Jr. et al. disclosure, among other techniques, it has been found that the cross-sectional outer or peripheral contour of the filled cable core is irregular. When a core wrap is applied thereto, it must conform closely to the irregular contour of the cable core in order to avoid creating voids between the periphery of the cable core and the subsequently applied core wrap. These voids can be minimized by utilizing a supple and easily formable core wrap material, for example, a core wrap formed from randomly arranged nonhygroscopic fibers of the type disclosed and claimed in R. S. Elliott U.S. Pat. No. 3,509,269. However, though the use of an easily formable core wrap minimizes the creation of any voids between the core wrap and the cable core, it does not avoid them completely.
Furthermore, the combination of a cable core enclosed in a highly formable core wrap, has an irregular peripheral contour, making it difficult to form an armor sheath, for example, a sheath of corrugated aluminum or steel, in water tight relationship about the cable core and the core wrap. As a result, the finished cable may not be completely impervious to water ingress and migration.
L. D. Moody U.S. Pat. No. 3,733,255 teaches passing a wrapped cable core having an irregular peripheral contour longitudinally through an elongated forming tube in which an armor sheath is formed about the core and introducing jelly-like waterproofing compound into the forming tube at a point spaced from its entrance end and under relatively high pressure to produce a waterproof layer of the compound which coats the wrapped core and provides a smooth cylindrical surface about which the sheath can be formed as the wrapped cable core assembly exits from the forming tube. The pressure at which the compound is introduced into the forming tube forces the compound between the overlapped edged portions of the sheath to seal and waterproof the seam formed by the edge portions. This method, however, does not insure the absence of voids or air pockets between the core wrap and the filled cable core.